Raised Bed Sizes & Materials
A reference guide for sizing and building raised garden beds. All dimension recommendations follow Mel Bartholomew's reach principle (beds ≤4 ft wide so no stepping in is required) and standard lumber dimensions.
Standard dimensions
| Size | Sq ft | Best for | Notes |
|---|---|---|---|
| 4 × 4 ft | 16 | Beginners, limited space, square-foot gardening grids | Maximum 2-ft reach from any side — no need to step in. Fits 16 one-foot SFG cells. |
| 4 × 8 ft | 32 | Most popular size; fits a standard 10 × 12 ft yard section | Mel Bartholomew's recommended starter size in Square Foot Gardening 3rd ed. Reachable from both long sides. |
| 4 × 12 ft | 48 | Established gardeners; more variety without another bed | Keep width ≤4 ft to maintain the no-step-in rule. 48 one-foot SFG cells. |
| 3 × 6 ft | 18 | Narrow spaces, children's gardens, accessibility | 3-ft width allows access from one side only — useful against walls or fences. |
Source: Bartholomew, Mel. All New Square Foot Gardening, 3rd ed. Cool Springs Press.
Minimum soil depth by crop type
Minimum viable depth. Requires good native soil underneath or a weed barrier with amended subsoil.
Recommended for general vegetable growing. Enough soil volume to buffer moisture and temperature.
Minimum for taproot crops. Go 16 in. for long carrot varieties (e.g., Imperator types, 8+ in. roots).
Required for deep-rooted perennials. Rarely practical with standard lumber — consider cinder block or gabion.
Source: Old Farmer's Almanac — raised bed soil depth recommendations.
Material comparison
Untreated cedar
Pros: Naturally rot-resistant (lifespan 10–20 yr), safe for edibles, attractive appearance
Cons: Higher cost than pine; availability varies by region
The most recommended choice for food gardens. Western red cedar (Thuja plicata) contains thujaplicin, a natural preservative. Source: Old Farmer's Almanac raised bed materials guide.
Untreated pine
Pros: Lowest material cost, widely available
Cons: Lifespan 3–7 years without treatment; rots faster in humid climates
A practical first-bed choice if budget is a constraint. Avoid treated lumber (ACQ, CA-B) for edible beds unless labeled as acceptable by the manufacturer for food contact.
Galvanized steel / Corten steel
Pros: 30+ year lifespan, pest-proof, clean aesthetic
Cons: Higher upfront cost; galvanized zinc coating may leach trace amounts into soil over decades at very high temperatures
The New Zealand food-safety standard NZS 4131 covers galvanized steel for water contact; zinc leaching into edible-garden soil is considered negligible at garden scale by current research.
Concrete block / cinder block
Pros: Very low cost, durable, allows deep beds without full lumber sides
Cons: Aesthetic; older cinder blocks may contain fly ash — source blocks manufactured after 2005 to avoid heavy-metal concerns
Stack dry (no mortar) for easy reconfiguration. Fill cavities with soil to create extra growing space.
Sources
- Bartholomew, Mel. All New Square Foot Gardening, 3rd ed. Cool Springs Press.
- Old Farmer's Almanac — “How to Build a Raised Garden Bed.” almanac.com
- Cornell Cooperative Extension — raised bed construction and material safety guides.